Displacement control valve for variable displacement compressor

ABSTRACT

A displacement control valve for a variable displacement compressor includes a valve hole partially forming a supply passage or a bleed passage of the compressor and a valve body having a cross-sectional area changed portion that is movable into and out of the valve hole. The cross-sectional area changed portion has a minimum cross-sectional area portion and a maximum cross-sectional area portion. The cross-sectional area changed portion is shaped so that the cross-sectional area of the cross-sectional area changed portion increases from the minimum cross-sectional area portion to the maximum cross-sectional area portion. The minimum cross-sectional area portion initially enters into the valve hole when the cross-sectional area changed portion is moved into the valve hole. The maximum cross-sectional area portion is movable into the valve hole. The valve hole is closed when the maximum cross-sectional area portion is positioned in the valve hole.

BACKGROUND OF THE INVENTION

The present invention relates to a displacement control valve used for a variable displacement compressor that adjusts the pressure in a pressure control chamber by introducing refrigerant in the discharge pressure region of the compressor into the pressure control chamber through a supply passage and releasing the refrigerant in the pressure control chamber to the suction pressure region of the compressor through a bleed passage, thereby to control displacement of the compressor.

In a variable displacement compressor having a pressure control chamber that accommodates therein a swash plate whose inclination angle is variable, the inclination angle of the swash plate decreases as the pressure in the pressure control chamber rises. This decrease of the inclination angle increases the stroke of a piston thereby to increase the displacement of the compressor. On the other hand, the inclination angle of the swash plate increases as the pressure in the pressure control chamber falls. This increase of the inclination angle decreases the stroke of the piston thereby to decrease the displacement of the compressor.

Unexamined Japanese Patent Publication No. 2001-349278 discloses a displacement control valve having a valve body which is operable to open and close a supply passage through which a refrigerant gas in the discharge pressure region of the compressor is introduced into a crank chamber (or pressure control chamber). The valve body has a tapered portion which is movable to be brought into contact with a valve seat thereby to close a valve hole. When the valve body is moved or shifted in the direction that opens the valve hole, the amount of the refrigerant flowing from the discharge pressure chamber to the crank chamber increases. Thus, the pressure in the crank chamber rises, thereby decreasing the displacement of the compressor. On the other hand, when the valve body is shifted in the direction that closes the valve hole, the amount of the refrigerant flowing from the discharge pressure chamber to the crank chamber decreases. Thus, the pressure in the crank chamber falls, thereby increasing the displacement of the compressor.

When the valve body of the above displacement control valve is shifted in the direction for closing the valve hole, the tapered portion of the valve body is moved with the minimum-diameter portion thereof entering into the valve hole, until the tapered portion of the valve body is brought into contact at any intermediate-diameter portion thereof with the valve seat or the edge of opening of the valve hole. Since the maximum-diameter portion of the tapered portion of the valve body is larger than the inner diameter of the valve hole, the movement of the valve body is stopped before the maximum-diameter portion of the tapered portion reaches the valve seat. When the valve hole is opened, the refrigerant gas in the discharge pressure region flows past the tapered portion of the valve body in the direction from the minimum diameter portion to the maximum diameter portion. Thus, the tapered portion of the valve body is subjected to a pressure which is substantially the same as the discharge pressure of the compressor and acts on the valve body in the direction which causes an increase of the opening of the valve hole. On the other hand, the pressure in the crank chamber (or control pressure) acts on the valve body in the direction opposite to the above pressure.

The pressure of refrigerant gas present adjacent to the part of the valve body which protrudes radially outward beyond the inner peripheral surface of the valve hole as seen in the moving direction (or the axial direction) of the valve body, or whose diameter is greater than the inner diameter of the valve hole, is varied depending on the opening degree of the valve hole when the valve hole is opened. Namely, the pressure acting on the above protruding part of the tapered portion is varied according to the opening degree of the valve hole. Such pressure varying with the valve opening will affect the difference of pressures acting on the valve body in opposing directions and hence the accuracy of displacement controlling of the compressor.

The present invention is directed to a displacement control valve that contributes to improvement in controllability of the displacement of a variable displacement compressor.

SUMMARY OF THE INVENTION

According to the present invention, a displacement control valve is used for a variable displacement compressor that adjusts a pressure in a pressure control chamber by introducing a refrigerant in a discharge pressure region into the pressure control chamber through a supply passage and releasing the refrigerant in the pressure control chamber to a suction pressure region through a bleed passage, thereby controlling displacement of the compressor. The displacement control valve includes a valve hole and a valve body. The valve hole partially forms the supply passage or the bleed passage. The valve body has a cross-sectional area changed portion that is movable into and out of the valve hole. The cross-sectional area changed portion has a minimum cross-sectional area portion and a maximum cross-sectional area portion. The cross-sectional area changed portion is shaped so that a cross-sectional area of the cross-sectional area changed portion increases from the minimum cross-sectional area portion to the maximum cross-sectional area portion. The minimum cross-sectional area portion initially enters into the valve hole when the cross-sectional area changed portion is moved into the valve hole. The maximum cross-sectional area portion is movable into the valve hole. The valve hole is closed when the maximum cross-sectional area portion is positioned in the valve hole.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the present invention that are believed to be novel are set forth with particularity in the appended claims. The invention together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which:

FIG. 1A is a longitudinal cross-sectional view of a compressor of a first preferred embodiment according to the present invention;

FIG. 1B is a cross-sectional view of a hinge mechanism of the compressor of the first preferred embodiment;

FIG. 2A is a cross-sectional view of a displacement control valve of the first preferred embodiment;

FIG. 2B is a partially enlarged cross-sectional view of the displacement control valve of the first preferred embodiment when a valve hole is blocked;

FIG. 3 is a partially enlarged cross-sectional view of the displacement control valve of the first preferred embodiment when the valve hole is opened;

FIG. 4 is a partially enlarged cross-sectional view of the displacement control valve of the first preferred embodiment when the valve hole is fully opened;

FIG. 5 is a cross-sectional view of a displacement control valve of a second preferred embodiment according to the present invention;

FIG. 6 is a cross-sectional view of a displacement control valve of a third preferred embodiment according to the present invention; and

FIG. 7 is a cross-sectional view of a displacement control valve of a fourth preferred embodiment according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following will describe a first preferred embodiment according to the present invention with reference to FIGS. 1A through 4. Referring to FIG. 1A, a variable displacement compressor 10 has a housing assembly which includes a cylinder block 11, a front housing 12 and a rear housing 13. The front housing 12 is connected to the front end (the left end as seen in FIG. 1) of the cylinder block 11. The rear housing 13 is connected to the rear end (the right end as seen in FIG. 1) of the cylinder block 11 through a valve plate 14, valve plate forming plates 15 and 16 and a retainer forming plate 17.

The front housing 12 and the cylinder block 11 cooperate to define therein a pressure control chamber 121 through which a rotary shaft 18 extends. The rotary shaft 18 is supported by the front housing 12 and the cylinder block 11 via radial bearings 19 and 20. The rotary shaft 18 extends out of the front housing 12 and is driven to rotate by a vehicle engine E as an external drive source via an electromagnetic clutch (not shown).

A lug plate 21 is secured to the rotary shaft 18. A swash plate 22 is supported by the rotary shaft 18 in such a way that it is slidable in the axial direction of the rotary shaft 18 and inclinable relative to the axis of the rotary shaft 18. A hinge mechanism 23 is provided between the swash plate 22 and the lug plate 21 for allowing the swash plate 22 to incline relative to the lug plate 21 and transmitting the rotation of the rotary shaft 18 to the swash plate 22. As shown in FIG. 1B, the hinge mechanism 23 includes a pair of arms 212 and 213 extending from the lug plate 21 toward the swash plate 22 and a pair of projections 221 and 222 extending from the swash plate 22 toward the lug plate 21. The projections 221 and 222 are inserted in a recess 214 formed between the paired arms 212 and 213 and movable in the recess 214. The bottom of the recess 214 provides a cam surface 211 on which the ends of the projections 221 and 222 are slidable. The above-described arrangement of the paired arms 212 and 213, the paired projections 221 and 222 and the cam surface 211 permits the swash plate 22 to incline relative to the axis of the rotary shaft 18 and also to rotate with the rotary shaft 18. The inclination of the swash plate 22 is guided with the projections 221 and 222 sliding on the cam surface 211 and the swash plate 22 sliding on the rotary shaft 18.

As the center portion of the swash plate 22 moves toward the lug plate 21, the inclination angle of the swash plate 22 increases. The maximum inclination of the swash plate 22, which is shown by solid line in FIG. 1A, is restricted by contact of the swash plate 22 with the lug plate 21. The minimum inclination of the swash plate is shown by chain double-dashed line in FIG. 1A.

The cylinder block 11 has formed therethrough a plurality of cylinder bores 111 in which pistons 24 are received. The rotation of the swash plate 22 is converted into the reciprocating movement of the piston 24 via a pair of shoes 25.

The rear housing 13 has formed therein a suction chamber 131 as a suction pressure region and a discharge chamber 132 as a discharge pressure region. A suction port 141 is formed in the valve plate 14, the valve plate forming plate 16 and the retainer forming plate 17, respectively. A discharge port 142 is formed in the valve plate 14 and the valve forming palate 15, respectively. The valve forming plate 15 has formed therein a suction valve 151, and the valve forming plate 16 has formed therein a discharge valve 161. As the piston 24 moves leftward in its corresponding cylinder bore 111 as seen in FIG. 1A, a refrigerant gas is drawn from the suction chamber 131 into the cylinder bore 111 through the suction port 141 while pushing open the suction valve 151. As the piston 24 moves rightward in the cylinder bore as seen in FIG. 1A, on the other hand, the refrigerant gas is compressed and discharged out of the cylinder bore 111 into the discharge chamber 132 through the discharge port 142 pushing open the discharge valve 161. The discharge valve 161 then comes into contact with a retainer 171 formed in the retainer forming plate 17 thereby to restrict the opening degree of the discharge valve 161.

The rear housing 13 has formed therein a suction passage 26 through which the refrigerant gas before compression is introduced into the suction chamber 131. The rear housing 13 has also formed therein a discharge passage 27 through which the compressed refrigerant gas is delivered out of the discharge chamber 132. The suction passage 26 and the discharge passage 27 are connected by an external refrigerant circuit 28 in which a condenser 29 for removing heat from the refrigerant gas, an expansion valve 30 and an evaporator 31 for allowing the refrigerant to absorb the ambient heat are disposed. The expansion valve 30 is operable to regulate the flow rate of the refrigerant according to variation in the temperature of the refrigerant gas at the outlet of the evaporator 31. A throttle 281 is disposed in the external refrigerant circuit 28 between the discharge passage 27 and the condenser 29. The part of the external refrigerant circuit 28 between the discharge passage 27 and the throttle 281 is referred to as an external refrigerant circuit 28A, and the part of the external refrigerant circuit 28 between the throttle 281 and the condenser 29 is referred to as an external refrigerant circuit 28B.

An electromagnetic displacement control valve 32 is installed in the rear housing 13. As shown in FIG. 2A, the displacement control valve 32 has a solenoid 34 including a fixed core 35, a coil 36 and a movable core 37. Supplying an electric current to the coil 34, the fixed core 35 is magnetized to attract the movable core 37 thereto. Operation of the solenoid 34 is controlled by a controller C (shown in FIG. 1A) with electric current. In this preferred embodiment, the solenoid 34 is controlled by the controller C with duty ratio. A transmitting rod 38 is secured to the movable core 37.

The displacement control valve 32 includes a valve housing 39 which has a valve hole forming wall 40. The valve hole forming wall 40 has formed therein a valve hole 41 having a circumferential wall surface 411 and a uniform diameter. A chamber 42 is formed between the valve hole forming wall 40 and the movable core 37 in the valve housing 39. The valve hole 41 communicates with the chamber 42 which in turn communicates with the pressure control camber 121 through a passage 43 formed in the rear housing 13 and the cylinder bore 11. Furthermore, the chamber 42 communicates with a clearance 59 formed between the movable core 37 and the fixed core 35 through a passage 351. The chamber 42 also communicates with a back pressure space 60 formed behind the movable core 37 through the passage 351 and a passage 371. Namely, the pressure in the pressure control chamber 121 prevails in the back pressure space 60 through the passage 43, the chamber 42, and the passages 351 and 371.

Referring to FIG. 2B, the transmitting rod 38 has a valve body 44 formed integrally therewith. The valve body 44 includes a cylindrical portion 441 and a tapered portion 442. The tapered portion 442 is shaped so that its diameter decreases from the chamber 42 toward the valve hole 441, or is tapered toward the valve hole 441. The tapered portion 442 has its maximum-diameter portion 443 at the boundary between the cylindrical portion 441 and the tapered portion 442 and its minimum-diameter portion 444 at the boundary between the tapered portion 442 and the cylindrical reduced diameter portion 381 of the transmitting rod 38. Namely, the tapered portion 442 is shaped so that its cross sectional area increases from the minimum-diameter portion 444 as a minimum cross-sectional area portion toward the maximum-diameter portion 443 as a maximum cross-sectional area portion.

The cylindrical portion 441 of the valve body 44 is slidable in the valve hole 41. With part of the cylindrical portion 441 (or the maximum-diameter portion 443) positioned in the valve hole 41 as shown in FIG. 2A, a minute clearance is formed between the inner circumferential wall surface 411 of the valve hole 41 and the cylindrical portion 441 of the valve body 44. Due to the presence of this minute clearance, the cylindrical portion 441 is slidable in the valve hole 41. This minute clearance also allows the refrigerant gas in the valve hole 41 to flow slightly therethrough. To be more specific, with part of the cylindrical portion 441 (or the maximum-diameter portion 443) positioned in the valve hole 41, the valve hole 41 is not closed completely, but loosely so as to allow a slight flow of the refrigerant gas therethrough.

As shown in FIG. 2A, the transmitting rod 38 in the chamber 42 is provided with a spring seat 52 and a spring 53 is installed on the valve body 44 between the spring seat 52 and the valve hole forming wall 40. The transmitting rod 38 is urged by the spring force of the spring 53 in the direction which causes the movable core 37 to move away from the fixed core 35.

A first pressure sensing chamber 45 and a second pressure sensing chamber 46 are defined in the valve housing 39 and divided by a bellows 47 as a displacement body. The bellows 47 has its fixed end connected to an end wall 48 of the valve housing 39 and the opposite movable end connected to the reduced diameter portion 381 of the transmitting rod 38. The transmitting rod 38 is movable in conjunction with the bellows 47.

The first pressure sensing chamber 45 communicates with the external refrigerant circuit 28A upstream of the throttle 281 through a pressure introducing passage 49, and the second pressure sensing chamber 46 communicates with the external refrigerant circuit 28B downstream of the throttle 281 through a pressure introducing passage 50. The pressure in the external refrigerant circuit 28A upstream of the throttle 281 is introduced into the first pressure sensing chamber 45, and the pressure in the external refrigerant circuit 28B downstream of the throttle 281 and upstream of the condenser 29 is introduced into the second pressure sensing chamber 46. The pressure in the first pressure sensing chamber 45 and the pressure in the second pressure sensing chamber 46 act against each other through the bellows 47.

When there is a flow of the refrigerant gas in the external refrigerant circuits 28A and 28B, the pressure of refrigerant gas in the external refrigerant circuit 28A upstream of the throttle 281 is larger than that in the external refrigerant circuit 28B downstream of the throttle 281 and upstream of the condenser 29. As the flow rate of the refrigerant gas in the external refrigerant circuits 28A and 28B (or in the discharge pressure region) increases, the difference of pressures between the upstream and downstream of the throttle 281 increases, so that the pressure difference between the first and second pressure sensing chambers 45 and 46 increases. On the other hand, as the flow rate of the refrigerant gas in the external refrigerant circuits 28A and 28B (or in discharge pressure region) decreases, the pressure difference between the upstream and downstream of the throttle 281 decreases, so that the pressure difference between the first and second pressure sensing chambers 45 and 46 decreases. The pressure difference between the first and second pressure sensing chambers 45 and 46 produces a force urging the transmitting rod 38 in the direction from the valve hole 41 toward the chamber 42, or downward as seen in FIG. 2A.

The first and second pressure sensing chambers 45 and 46 and the bellows 47 constitute a pressure sensing means 51 of the present invention for sensing the pressure difference between the external refrigerant circuit 28A upstream of the throttle 281 and the external refrigerant circuit 28B downstream of the throttle 281 and upstream of the condenser 29. The opening and closing operation of the valve hole 41 depends on the balance among various forces such as the electromagnetic force generated by the solenoid 34, the urging force resulting from the pressure in the back pressure space 60 (or control pressure) and acting on the transmitting rod 38 in the direction that closes the valve hole 41, the spring force of the spring 53 and the urging force of the pressure sensing means 51.

The pressure sensing means 51 is operable to sense the pressure at a first point (or the external refrigerant circuit 28A) in the discharge pressure region (or the external refrigerant circuits 28A and 28B) and the pressure at a second point (or the external refrigerant circuit 28B) in the discharge pressure region and to adjust the position of the transmitting rod 38 or the valve body 44 based on the difference of pressures between the first and second points.

As shown in FIG. 1A, the controller C, which controls the solenoid 34 of the displacement control valve 32 with electric current (duty ratio), supplies electric current to the solenoid 34 while the air conditioner switch 54 is turned on. With the air conditioner switch 54 turned off, the controller C stops supplying the electric current to the solenoid 34. A room temperature setting device 55 and a room temperature detector 56 are electrically connected to the controller C. With the air conditioner switch turned on, the controller C controls the electric current supplied to the solenoid 34 based on the difference between a target temperature set by the room temperature setting device 55 and a temperature then detected by the room temperature detector 56. As the duty ratio is increased, the transmitting rod 38 (the valve body 44) moves in the direction from the chamber 42 toward the valve hole 41, or upward as seen in FIG. 2A.

When the maximum-diameter portion 443 of the valve body 44 is moved out of the valve hole 41 to open the valve hole 41 as shown in FIGS. 3 and 4, part of the refrigerant gas in the external refrigerant circuit 28B flows into the pressure control chamber 121 through a supply passage 57 which includes the pressure introducing passage 50, the second pressure sensing chamber 46, the valve hole 41, the chamber 42 and the passage 43. When the maximum-diameter portion 443 of the valve body 44 is moved into the valve hole 41 thereby to close the valve hole 41 as shown in FIG. 2B, the refrigerant flow from the external refrigerant circuit 28B through the supply passage 57 to the pressure control chamber 121 is blocked.

As shown in FIG. 1A, the pressure control chamber 121 communicates with the suction chamber 131 through a bleed passage 58 that is formed in the cylinder block 11, the valve forming plate 15, the valve plate 14, the valve forming plate 16 and the retainer forming plate 17. Thus, the refrigerant gas in the pressure control chamber 121 can flow out thereof into the suction chamber 131 through the bleed passage 58. The pressure in the pressure control chamber 121 is varied or adjusted by controlling the flow of refrigerant gas flowing from the external refrigerant circuit 28B into the pressure control chamber 121 through the supply passage 57 and the flow of refrigerant gas flowing from the pressure control chamber 121 into the suction chamber 131 through the bleed passage 58.

In FIG. 2A, the maximum amount of the electric current is supplied to the solenoid 34 and the valve hole 41 is closed, accordingly. In this state, the amount of the refrigerant gas flowing from the external refrigerant circuit 28B through the supply passage 57 into the pressure control chamber 121 is substantially zero. The refrigerant gas in the pressure control chamber 121 then flows out into the suction chamber 131 through the bleed passage 58. Thus, the pressure in the pressure control chamber 121 falls, so that the swash plate 22 is tilted to its maximum angle position and the piston 14 is moved for its maximum length of stroke, accordingly, with the result that the displacement of the compressor 10 becomes the maximum.

In FIG. 3, the amount of electric current supplied to the solenoid 34 is less than the maximum and the valve hole 41 is opened. In this state, the refrigerant gas in the external refrigerant circuit 28B flows into the pressure control chamber 121 through the supply passage 57, thereby increasing the pressure in the pressure control chamber 121. Thus, the inclination angle of the swash plate 22 decreases from the maximum angle.

In FIG. 4, the electric current supply to the solenoid 34 is stopped and, therefore, the valve hole 41 is fully opened. In this state, the amount of the refrigerant gas flowing from the external refrigerant circuit 28B through the supply passage 57 into the pressure control chamber 121 is increased thereby to further increase the pressure in the pressure control chamber 121. Thus, the inclination angle of the swash plate 22 becomes the minimum. As apparent from the foregoing description, the displacement control valve 32 is of a normally-opened type according to which the valve hole 41 is opened when no electric current is supplied to the solenoid 34.

The following advantageous effects are obtained according to the first preferred embodiment.

(1-1) With the maximum-diameter portion 443 of the tapered portion 442 positioned out of the valve hole 41, the valve hole 41 is opened. Unlike the displacement control valve of the aforementioned prior art, no part of the tapered portion 442 of the valve body 44 protrude radially outward beyond the inner peripheral surface of the valve hole 41 as seen in the moving direction (or the axial direction) of the valve body 44.

Let us assume that part of the tapered portion 442 of the valve body 44 protrudes radially outward beyond the inner peripheral surface of the valve hole 41 as seen in the moving direction of the valve body 44 or that the diameter of the maximum-diameter portion 443 is greater than the inner diameter of the valve hole 41. The pressure of refrigerant gas present adjacent to such imaginary protruding part of the tapered portion 442 (or the part whose outer diameter is larger than the inner diameter of the valve hole 41) is varied depending on the opening degree of the valve hole 41 when the valve hole 41 is opened. Namely, the pressure acting on the protruding part of the tapered portion 442 is varied according to the opening degree of the valve hole 41. Such pressure varying with the valve opening will affect the difference between the pressure acting on the tapered portion 442 (or the pressure that is substantially the same as the discharge pressure) and the pressure in the back pressure space 60 acting on the valve body 44 through the transmitting rod 38 (or the control pressure), with the result that the movement of the valve body 44 (or the transmitting rod 38) becomes unstable, thereby deteriorating the controllability of the displacement of the compressor 10. When the valve hole 41 is changed from the closed state to the opened state, the pressure of the refrigerant gas then flowing from the valve hole 41 to the chamber 42 suddenly acts on the protruding part of the tapered portion 442, which may cause excessive movement of the valve body 44. Namely, since the area of the tapered portion 442 which receives the pressure of the refrigerant gas flowing from the valve hole 41 to the chamber 42 rapidly increases, the valve body 44 may move excessively. This deteriorates the controllability of the displacement of the compressor 10.

In the displacement control valve of the above-described embodiment according to the present invention, no part of the tapered portion 442 protrudes radially outward beyond the inner peripheral surface of the valve hole 41 as seen in the moving direction of the valve body 44. This structure prevents the difference between the pressure acting on the tapered portion 442 (or the pressure corresponding to the discharge pressure) and the pressure acting on the valve body 44 from the opposite direction (or the control pressure) from being changed significantly by variation in the opening degree of the valve hole 41. As a result, the controllability of the displacement of the compressor 10 is improved.

(1-2) If the cross-sectional area of the valve hole 41 that forms a part of the supply passage 57 could be changed as desired, the displacement of the compressor 10 could be controlled elaborately. The tapered portion 442 having the conical peripheral surface is advantageous for changing the cross-sectional area of the valve hole 41 in accordance with the position of the valve body 44 in the valve hole 41.

(1-3) With the cylindrical portion 441 (the maximum-diameter portion 443) positioned in the valve hole 41, a minute clearance is formed between the circumferential wall surface 411 of the valve hole 41 and the cylindrical portion 441 of the valve body 44. A small amount of refrigerant gas flows from the second pressure sensing chamber 46 into the chamber 42 through this minute clearance. Thus, the pressure in the chamber 42 adjacent to the valve hole 41 is larger than that in the state where the valve hole is completely closed by the valve body as in the case of the Unexamined Japanese Patent Publication No. 2001-349278 where the refrigerant gas is completely prevented from flowing from the valve hole to the chamber. Namely, the provision of the minute clearance between the circumferential wall surface 411 of the valve hole 41 and the cylindrical portion 441 reduces the change of the pressure difference (or the difference between the pressures acting on the tapered portion 442 and on the valve body 44 in opposing directions), which occurs when the maximum-diameter portion 443 is moved out of the valve hole 41.

The following will describe a second preferred embodiment of the present invention with reference to FIG. 5. Like or same parts or elements are referred to by the same reference numerals as those which have been used in the first preferred embodiment.

Referring to FIG. 5, the displacement control valve 32A has a valve housing 39 that defines therein a discharge pressure introducing chamber 61. The discharge pressure introducing chamber 61 communicates through a passage 62 with the external refrigerant circuit 28C that connects the discharge chamber 132 and the condenser 29. A spring seat 63 and a spring 64 are disposed in the discharge pressure introducing chamber 61. The spring 64 is interposed between the spring seat 63 and the end wall 48 of the valve housing 39, and the reduced diameter portion 381 of the transmitting rod 38 is connected to the spring seat 63. The spring 64 urges the transmitting rod 38 in the direction from the valve hole 41 toward the chamber 42, or downward as seen in FIG. 5. The transmitting rod 38 is also urged by the spring 53 in the same direction.

The pressure in the discharge pressure introducing chamber 61 is substantially the same as that in the external refrigerant circuit 28C as a discharge pressure region (or the discharge pressure). The pressure in the chamber 42 and the back pressure space 60 is substantially the same as that in the pressure control chamber 121 (or the control pressure). The transmitting rod 38 receives the pressure in the discharge pressure introducing chamber 61 at one end thereof on the side of the reduced diameter 381 and the pressure in the back pressure space 60 (or the control pressure) at the other end thereof. More specifically, the transmitting rod 38 receives a load F1 resulting from the pressure in the back pressure space 60 and determined by multiplying the cross sectional area of the cylindrical portion 441 of the valve body 44 by the control pressure. The load F1 acts on the transmitting rod 38 in the direction from the chamber 42 toward the valve hole 41, or upward as seen in FIG. 5. The transmitting rod 38 also receives a load F2 resulting from the discharge pressure in the discharge pressure introducing chamber 61 and determined by multiplying the cross sectional area of the cylindrical portion 441 by the discharge pressure. The load F2 acts on the transmitting rod 38 in the direction opposite to the load F1. Namely, the load F1 and the load F2 act against each other through the transmitting rod 38. Therefore, the transmitting rod 38 is urged by the load difference (or F2−F1) in the direction from the valve hole 41 toward the chamber 42, or downward as seen in FIG. 5. The load difference (F2−F1) acts against the electromagnetic force of the solenoid 34.

The opening and closing operation of the valve hole 41 depends on the balance among various forces such as the electromagnetic force generated by the solenoid 34, the spring forces of the springs 53 and 64 and the urging force resulting from the load difference (F2−F1). As the pressure difference between the discharge pressure and the control pressure increases, the load difference (F2−F1) becomes large and the transmitting rod 38 moves downward as seen in FIG. 5, accordingly. On the other hand, as the pressure difference between the discharge pressure and the control pressure decreases, the load difference (F2−F1) becomes small, so that the transmitting rod 38 moves upward as seen in FIG. 5.

According to the second preferred embodiment, the same advantageous effects as those in the first preferred embodiment are obtained and the following additional effect is also obtained.

(2-1) In the displacement control valve 32A which is formed so that the pressure in the discharge pressure introducing chamber 61 acts against the pressure in the back pressure space 60 (or the control pressure) through the transmitting rod 38, the pressure difference between the discharge pressure and the control pressure is the object to be controlled. The displacement control valve 32A is controlled in such a manner that the pressure difference between the discharge pressure and the control pressure balances with the electromagnetic force at the solenoid 34. Since the displacement control valve 32A of FIG. 5 dispenses with the pressure sensing means 51 using the bellows 47 as in the first preferred embodiment, the displacement control valve 32A of the second preferred embodiment is simpler in structure than the displacement control valve 32 including the pressure sensing means 51.

The following will describe a third preferred embodiment of the present invention with reference to FIG. 6. Like or same parts or elements are referred to by the same reference numerals as those which have been used in the first preferred embodiment.

Referring to FIG. 6, the displacement control valve 32B has a chamber forming housing 65 that has formed therein a suction pressure introducing chamber 651. The spring 53 is disposed in the suction pressure introducing chamber 651 and urges the transmitting rod 38 in the direction from the valve hole 41 toward the chamber 42. The suction pressure introducing chamber 651 communicates with the suction chamber 131 through a passage 66. The suction pressure introducing chamber 651 also communicates with the back pressure space 60 through the passages 351 and 371. The pressure in the suction chamber 131 (or suction pressure) is introduced into the back pressure space 60 through the passage 66, the suction pressure introducing chamber 651 and the passages 351 and 371. Thus, the back pressure space 60 is a part of the suction pressure region.

The transmitting rod 38 receives a load F3 resulting from the suction pressure in the back pressure space 60 and determined by multiplying the cross sectional area of the cylindrical portion 441 of the valve body 44 by the suction pressure. The load F3 acts on the transmitting rod 38 in the direction from the chamber 42 toward the valve hole 41, or upward as seen in FIG. 6. The transmitting rod 38 also receives the load F2 resulting from the discharge pressure in the discharge pressure introducing chamber 61 and determined by multiplying the cross sectional area of the cylindrical portion 441 by the discharge pressure. The load F2 acts on the transmitting rod 38 in the direction from the valve hole 41 toward the chamber 42, or downward as seen in FIG. 6. Namely, the load F3 and the load F2 act against each other through the transmitting rod 38. Therefore, the transmitting rod 38 is urged by the load difference (or F2−F3) downward as seen in FIG. 6. The load difference (F2−F3) acts against the electromagnetic force of the solenoid 34.

The opening and closing operation of the valve hole 41 depends on the balance among various forces such as the electromagnetic force generated at the solenoid 34, the spring forces of the springs 53 and 64 and the urging force resulting from the load difference (F2−F3). As the pressure difference between the discharge pressure and the control pressure increases, the load difference (F2−F3) becomes large and the transmitting rod 38 moves downward as seen in FIG. 6, accordingly. On the other hand, as the pressure difference between the discharge pressure and the control pressure decreases, the load difference (F2−F3) becomes small, so that the transmitting rod 38 moves upward as seen in FIG. 6.

According to the third preferred embodiment, the same advantageous effects as those in the first preferred embodiment are obtained and the following additional effect is also obtained.

(3-1) In the displacement control valve 32B which is formed so that the pressure in the discharge pressure introducing chamber 61 acts against the pressure in the back pressure space 60 (or suction pressure) through the transmitting rod 38, the pressure difference between the discharge pressure and the suction pressure is the object to be controlled. The displacement control valve 32B is controlled in such a manner that the pressure difference between the discharge pressure and the suction pressure balances with the electromagnetic force at the solenoid 34. Since the displacement control valve 32B of FIG. 6 dispenses with the pressure sensing means 51 using the bellows 47 as in the first preferred embodiment, the displacement control valve 32B of the third preferred embodiment is simpler in structure than the displacement control valve 32 including the pressure sensing means 51.

The following will describe a fourth preferred embodiment of the present invention with reference to FIG. 7. Like or same parts of elements are referred to by the same reference numerals as those which have been used in the first preferred embodiment.

Referring to FIG. 7, the displacement control valve 32C has a chamber forming housing 67 and a housing 69. The chamber forming housing 67 has formed therein a control pressure introducing chamber 671 and a valve hole 673. The chamber forming housing 67 and the housing 69 cooperate to define a suction pressure introducing chamber 672. The control pressure introducing chamber 671 communicates with the suction pressure introducing chamber 672 through the valve hole 673.

The housing 69 accommodates therein a bellows 47 as a displacement body to which an auxiliary rod 68 is connected. The auxiliary rod 68 extends through a partition wall 691 of the housing 69 and further into the suction pressure introducing chamber 672. The auxiliary rod 68 has a reduced diameter portion 681 that extends through the valve hole 673 and further into the control pressure introducing chamber 671. The reduced diameter portion 681 is connected to the transmitting rod 38, and the auxiliary rod 68 is movable in conjunction with the transmitting rod 38.

The auxiliary rod 68 is formed integrally with a valve body 70 which includes a cylindrical portion 701 and a tapered portion 702. The tapered portion 702 is shaped so that its diameter decreases from the suction pressure introducing chamber 672 toward the valve hole 673, or is tapered toward the valve hole 673. The tapered portion 702 has its maximum-diameter portion 703 at the boundary between the tapered portion 702 and the cylindrical portion 701 and its minimum-diameter portion 704 at the boundary between the tapered portion 702 and the reduced diameter portion 681 of the auxiliary rod 68. Namely, the tapered portion 702 is shaped so that its cross-sectional area increases from the minimum-diameter portion 704 as a minimum cross-sectional area portion toward the maximum-diameter portion 703 as a maximum cross-sectional area portion.

The cylindrical portion 701 of the valve body 70 is slidable in the valve hole 673. With the cylindrical portion 701 (or the maximum-diameter portion 703) positioned in the valve hole 673, the valve hole 673 is closed, but a minute clearance is formed between the circumferential wall surface of the valve hole 673 and the cylindrical portion 701. This minute clearance permits the cylindrical portion 701 to slide in the valve hole 673. The minute clearance also allows the refrigerant gas in the valve hole 673 to flow therethrough slightly with the cylindrical portion 701 (or the maximum-diameter portion 703) positioned in the valve hole 673. Namely, with the cylindrical portion 701 (the maximum-diameter portion 703) positioned in the valve hole 673, the valve hole 673 is not completely but loosely closed, thereby allowing a slight flow of the refrigerant gas therethrough.

The control pressure introducing chamber 671 communicates with the pressure control chamber 121 through a passage 71, and the suction pressure introducing chamber 672 communicates with the suction chamber 131 through a passage 72. The passage 71, the control pressure introducing chamber 671, the valve hole 673, the suction pressure introducing chamber 672 and the passage 72 constitute a bleed passage 73 through which the refrigerant gas flows from the pressure control chamber 121 into the suction chamber 131. The discharge chamber 132 communicate with the pressure control chamber 121 through a supply passage 74.

The control pressure introducing chamber 671 communicates with the back pressure space 60 through the passages 351 and 371 and, therefore, the back pressure space 60 is a part of control pressure region. The opening and closing operation of the valve hole 673 depends on the balance among various forces such as the electromagnetic force generated by the solenoid 34, the urging force resulting from the pressure in the back pressure space 60 (or control pressure) which urges the transmitting rod 38 the direction that closes the valve hole 673, the spring force of the spring 53 in the control pressure introducing chamber 671 and the urging force of the pressure sensing means 51.

The controller C regulates the electric current supplied to the solenoid 34 (duty ratio) based on the temperature difference between a target temperature set by the room temperature setting device 55 and a room temperature then detected by the room temperature detector 56. As the duty ratio is increased, the transmitting rod 38 and the auxiliary rod 68 (the valve body 70) are moved in the direction from the control pressure introducing chamber 671 toward the valve hole 673.

In FIG. 7, the valve hole 673 of the displacement control valve 32C is fully opened (the minimum-diameter portion 704 is moved out of the valve hole 673) and the refrigerant gas in the pressure control chamber 121 flows out into the suction chamber 131 through the bleed passage 73. The refrigerant gas in the discharge chamber 132 flows into the pressure control chamber 121 through the supply passage 74. In the state where the valve hole 673 is fully opened, the pressure in the pressure control chamber 121 is low, so that the inclination angle of the swash plate 22 (cf. FIG. 1A) becomes the maximum. Accordingly, the piston 24 is reciprocated for the maximum length of stoke (cf. FIG. 1A), with the result that that the displacement of the compressor becomes the maximum.

With the electric current supply to the solenoid 34 stopped, the maximum-diameter portion 703 is moved into the valve hole 673 thereby to close the valve hole 673. In this state, no refrigerant gas flows from the pressure control chamber 121 into the suction chamber 131 through the bleed passage 73. Since the refrigerant gas in the discharge chamber 132 flows into the pressure control chamber 121 through the supply passage 74, the pressure in the pressure control chamber 121 is high in the state where the valve hole 673 is closed, so that the inclination angle of the swash plate 22 (cf. FIG. 1A) then becomes the minimum. Accordingly, the stroke of the piston 24 (cf. FIG. 1A) becomes the minimum, so that the displacement of the compressor becomes the minimum. The displacement control valve 32C is of a normally-closed type according to which the valve hole 673 is closed when no electric current is supplied to the solenoid 34.

According to the fourth preferred embodiment, the same advantageous effects as the paragraphs (1-2) and (1-3) in the first preferred embodiment are obtained. The following additional effect is also obtained.

(4-1) In the displacement control valve 32C of the fourth preferred embodiment, no part of the tapered portion 702 protrudes radially outward beyond the inner peripheral surface of the valve hole 673 as seen in the moving direction (or the axial direction) of the valve body 70. This structure prevents the difference between the pressure acting on the tapered portion 702 (or the pressure corresponding to the control pressure) and the pressure acting on the valve body 70 from the opposite direction (or the urging force from the pressure sensing means 51) from being changed significantly by variation in the opening degree of the valve hole 673. As a result, the controllability of the displacement of the compressor 10 (cf. FIG. 1A) is improved.

According to the present invention, the following alternative embodiments may be practiced.

(1) In the foregoing embodiments, the intermediate portion between the maximum-diameter and minimum-diameter portions of the valve body is formed with a taper so that the diameter of the intermediate portion of the valve body is changed linearly. However, this intermediate portion of the valve body may be formed such that the diameter thereof is changed in a non-linear manner.

(2) The circumferential wall surface of the valve hole may be formed with a taper. In this case, the minimum diameter portion initially enters into the tapered valve hole when the valve body having the cross-sectional area changed portion is moved into the tapered valve hole.

(3) The bellows used as a part of the pressure sensing means in the first and fourth embodiments may be substituted by a diaphragm or a piston.

The present examples and embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein but may be modified within the scope of the appended claims. 

1. A displacement control valve used for a variable displacement compressor that adjusts a pressure in a pressure control chamber by introducing a refrigerant in a discharge pressure region into the pressure control chamber through a supply passage and releasing the refrigerant in the pressure control chamber to a suction pressure region through a bleed passage, thereby controlling displacement of the compressor, the displacement control valve comprising: a valve hole partially forming the supply passage or the bleed passage; and a valve body having a cross-sectional area changed portion that is movable into and out of the valve hole, wherein the cross-sectional area changed portion has a minimum cross-sectional area portion and a maximum cross-sectional area portion, wherein the cross-sectional area changed portion is shaped so that a cross-sectional area of the cross-sectional area changed portion increases from the minimum cross-sectional area portion to the maximum cross-sectional area portion, wherein the minimum cross-sectional area portion initially enters into the valve hole when the cross-sectional area changed portion is moved into the valve hole, wherein the maximum cross-sectional area portion is movable into the valve hole, and wherein the valve hole is closed when the maximum cross-sectional area portion is positioned in the valve hole.
 2. The displacement control valve according to claim 1, wherein the cross-sectional area changed portion has a conical peripheral surface.
 3. The displacement control valve according to claim 1, wherein a minute clearance is formed between the maximum cross-sectional area portion and a circumferential wall surface of the valve hole when the maximum cross-sectional area portion is positioned in the valve hole for allowing the refrigerant to flow therethrough slightly.
 4. The displacement control valve according to claim 1, wherein the valve hole is a part of the supply passage, and wherein the displacement control valve is adapted to open the valve hole when the compressor is at its minimum displacement.
 5. The displacement control valve according to claim 1, wherein the valve hole is a part of the bleed passage, and wherein the displacement control valve is adapted to close the valve hole when the compressor is at its minimum displacement.
 6. The displacement control valve according to claim 1, wherein the cross-sectional area changed portion is tapered toward the valve hole.
 7. The displacement control valve according to claim 1, further comprising a pressure sensing means operable to sense a pressure of a first point in the discharge pressure region and a pressure of a second point in the discharge pressure region and to regulate a position of the valve body based on pressure difference between the first and second points.
 8. The displacement control valve according to claim 7, wherein the pressure sensing means includes a first pressure sensing chamber, a second pressure sensing chamber and a displacement body that divides the first and second pressure sensing chambers, wherein the valve body is connected to the displacement body, wherein the pressure of the first point is introduced into the first pressure sensing chamber, and wherein the pressure of the second point is introduced into the second pressure sensing chamber.
 9. The displacement control valve according to claim 8, wherein the displacement body is a bellows.
 10. The displacement control valve according to claim 1, further comprising a rod connected to the valve body, wherein the displacement control valve is formed so that the rod receives the pressure in the discharge pressure region and the pressure in the pressure control chamber, and wherein a load resulting from the pressure in the discharge pressure region and a load resulting from the pressure in the pressure control chamber act against each other through the rod.
 11. The displacement control valve according to claim 1, further comprising a rod connected to the valve body, wherein the displacement control valve is formed so that the rod receives the pressure in the discharge pressure region and the pressure in the suction pressure region, and wherein a load resulting from the pressure in the discharge pressure region and a load resulting from the pressure in the suction pressure region act against each other through the rod.
 12. The displacement control valve according to claim 1, further comprising a solenoid for generating an electromagnetic force acting on the valve body. 